Transmission error is a potentially serious problem for a broadcast digital video such as a high definition television (HDTV) signal. For example, a broadcast television signal compressed by means of a sophisticated digital image compression algorithm may suffer severe image degradation due to moderate to high transmission channel impairments such as thermal noise. In systems employing motion compensation algorithms, as is common, the results of transmission channel impairments can be catastrophic.
Channel errors can be controlled by using error confinement techniques to contain errors within one or more known regions of the image. Once the error is contained, a variety of known error concealment techniques can be employed. Error confinement can be achieved by transmitting the data in transport blocks as is known. Transport block header data may include a code such as a cyclic redundancy code to provide a measure of error protection. The error code is typically capable of correcting only relatively small errors, though larger errors may be detected but not corrected. At a receiver, a transport block containing an error is flagged, and the region in the reconstructed image to which such transport block pertains can then be subjected to a process of error concealment.
Conventional error confinement and concealment techniques work well in the reconstructed image domain. In other words, the effect of the error on the reconstructed image is confined, and the error concealment is applied to the reconstructed image. Currently, most video compression systems rely substantially on temporal predictive algorithms to produce the desired data compression. In such cases, the parts of the transmitted data that are subject to transmission impairment are primarily motion information, compression parameters and residual image information (i.e., prediction error image information).
It is herein recognized that the residual image information often represents a significant portion of the total image information. As a result, transmission impairments are applied primarily to the residual image rather than to the reconstructed displayed image.